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As the fourth edition of this book goes to print, I am happy to present a much‐enhanced text, both in terms of the verbal discussion and the illustrated figures, which is offered in a similar pattern to its predecessors. The third edition of Orthodontic Treatment of Impacted Teeth, published in 2012, had 15 chapters. This new edition comprises 21 chapters, of which several are completely new and, together with the significant additions and improvements, the overall content is now approximately 60% larger.

Video clips and other 3D illustrations cannot be published in book form, thus preventing the printed literature from matching the advances in the recording of radiographic imaging that is now commonplace in dental schools, in radiographic imaging centres and in private dental offices. This is particularly so in relation to orthodontics, in general and to accurate positional and pathological diagnosis, that are so essential in the resolution of tooth impaction, in particular. In order to overcome these serious illustrative limitations, I have included a Companion website adjacent to the text, to enhance the orthodontist’s ability to use the existing presentation modes (secondary reconstructions), to extract the maximum information that is available in a cone beam CT scan. A number of 3D video clips are presented, to illustrate how to refine the diagnostic know‐how, which can only be to the benefit of the patient. These are embedded in PowerPoint presentations, with concise accompanying comment to highlight the salient points at issue. This should assist those who still have 3D comprehension difficulty in accurately locating the impacted tooth.

There are many new areas in the present text that feature aspects that have not been fully described in the literature to date. There are also a number of supposed truths that are shown to be spurious and contrary to our understanding of the biological process.

Just to mention a few of the many examples that the reader will find in this edition:

 Did you know that hooked roots are not a reason that teeth do not erupt (see Chapter 13)?

 Unerupted incisor teeth that have been severely damaged by trauma inflicted in infancy remain high in the maxilla adjacent to the nasal floor, neither growing their roots nor showing any signs of ever erupting into the mouth. Can these teeth be mechanically erupted? Will they develop roots of a sufficient length that will contribute to the tooth surviving into adulthood? Will the eruption of these teeth generate new bone that could naturally rehabilitate the formerly deficient alveolar ridge (see Chapter 6)?

 Instead of developing a long straight root, the severely traumatized central incisor in a 2‐year‐old child may develop a root that continues to grow at an acute angle to the calcified portion of the tooth, to form a tightly curved or angled dilaceration. The root continues to grow in the wrong direction, necessitating root canal treatment and root amputation to enable the orthodontist to re‐align the majority portion of the tooth. Perhaps there is a way to correct the direction of the further root growth and thereby achieve a normally apexified vital tooth with a perfect crown, indistinguishable from and aligned with its beautiful adjacent counterpart (see Chapter 6).

 There appears to be a cut‐off age of 9 years for the maxillary lateral incisor to develop at least half its normal root length. If there is less than a half root at this age, as seen in a small or peg‐shaped tooth, the chances that the unerupted canine will become the victim of eruption disturbance become notably exaggerated (see Chapter 6).

 Conventional wisdom has it that mandibular second and third molars are sometimes impacted because their roots are being ‘held down’ by entanglement with the inferior alveolar canal (mandibular branch of the trigeminal nerve). We maintain that this view is unfounded (see Chapter 13). It is more likely that another factor, such as invasive cervical root resorption (ICRR), enlarged dental follicle, crowding of adjacent teeth and even possibly pre‐eruption intra‐coronal resorption, represents the primary aetiology that prevents eruption (the ‘cause’). With the root apices then growing in cramped circumstances, in close proximity to pathological entities or anatomical limits, the further erratic development of the root ends inevitably results in entanglement with the nerve and vascular bundle (the ‘effect’).

 You have just finished the phase 1 treatment of a child, for the treatment of a cross‐bite or an impacted incisor or for maxillary anterior crowding, and he is now 8 years old. As the final flourish, you have aligned the incisors and paralleled their roots into their final adult orientation. The four incisors look beautiful and the parents are happy. In order to hold on to this delightful result, a fixed or removable retainer will need to be placed, until the child is ready for phase 2 treatment in 3–4 years’ time. The question that needs to be asked is: Will the ‘attention to detail’ at this early stage and the apparently laudable ‘intention to fully exploit the capabilities of an existing orthodontic appliance’ be to the patient’s overall benefit, or will they raise the spectre of iatrogenic damage in the long term, by potentially disturbing the eruption of the canine (see Chapters 6, 7 and 18)?

A word about the tooth‐numbering convention used in this book. For the most part, the narrative in this volume refers to the individual teeth by their full descriptive title. Thus, we may refer to an impacted maxillary left permanent canine tooth or an infra‐occluded deciduous mandibular second molar tooth – a six‐word definition for a very small entity. However, for the sake of brevity and particularly for the annotation of teeth in an illustration, an author will prefer to use a shortened code for each tooth. The numbering system we have used here is the Fédération Dentaire Internationale (FDI) numbering system. This system has been widely accepted in many parts of the world, being easy to understand, logical and adaptable to the various tooth groups. It is compatible with computerized representation and uses the same description of the teeth on either side and in either jaw in a symmetrical and rapidly recognizable manner.

The method assigns a two‐number code to each tooth. The first number defines the quadrant in which the tooth is found. Thus, the right maxillary quadrant, from midline to last molar, is given the number 1. The left maxillary quadrant is number 2; the left mandibular quadrant number 3; and the right mandibular quadrant number 4. The individual teeth are then numbered from 1 to 8, beginning from the midline and proceeding to the last molar. In this manner, all impacted canines will be recognized by the second number 3: a right maxillary canine would be denoted 13; a left mandibular second molar would be assigned 37; and a mandibular right lateral incisor 42. All four canines are rarely impacted in the same individual, but when this occurs, it will be appreciated that 13, 23, 33 and 43 will be more easily recognizable than the 6, 11, 22 and 27 of the so‐called ‘universal’ numbering system, which seems to have achieved acceptance largely in the USA. (We have occasionally used the hash sign # in front of the number, in order to clearly differentiate the tooth number from other numbers in the text.)

Similarly, numbering the deciduous teeth employs the quadrant system in the same order, labelled from 5 to 8 and the teeth numbered 1 to 5. Thus, the maxillary deciduous right central incisor is defined as 51 and an infra‐occluded mandibular right deciduous second molar is numbered 85.

I am grateful to each of my co‐authors for having enthusiastically responded to my invitation to write a specific chapter in this volume and for having submitted their finished manuscripts ahead of the deadline I set for them. The chapter on biomechanics as it relates to impacted teeth was written and illustrated by Dr Ulrich Kritzler, who is in private practice in Warendorf, Germany and a regular contributor to the international orthodontic literature. The rapidly expanding popularity of clear aligners in orthodontics prompted me to invite a discussion of their use, suitability and the limitations of their application to the treatment of cases with impacted teeth. This has been authored by Prof. Dror Aizenbud, Chair of the Unit for Orthodontics and Craniofacial Anomalies in Haifa, Israel.

For the past several years, I have availed myself of the expert services of Mr Amnon Leitner, perhaps the most knowledgeable and skilled master radiographic imaging technician I have ever had the good fortune to meet and to work with. I invited him to enlarge and update the chapter on diagnostic imaging, specifically with regard to cone beam computerized tomography. Several of his highly informative secondary reconstructions, 3D screenshots and video clips appear in that chapter and additional examples of his work may be seen in a number of other chapters.

I am grateful to Dr Athina‐Maria Mavridou of KU Leuven (University of Leuven) in Belgium, a trained endodontist and an accomplished research scientist, who provided helpful comment on the histopathological aspect of my description of invasive cervical root resorption. ICRR is a specific pathological entity in its own right and is discussed in Chapter 10. The positive diagnosis of ICRR has serious repercussions in relation to the treatment of impacted teeth, yet it is substantially uncharted territory and rarely recognized by orthodontists.

As in the second and third editions, I acknowledge the contribution to several chapters in the book, of Prof. Stella Chaushu, Chair of the Department of Orthodontics at the Hebrew University–Hadassah School of Dental Medicine, Jerusalem, Israel. For the past 25 years, our academic collaboration has achieved much in terms of basic and clinical research, particularly in the area of eruption disturbance. Tooth impaction has also been the subject of the many invited lectures and courses that we have conducted together internationally and this book largely represents the culmination of those years of endeavour, even from as early as 1964. It reflects many of the fruits of our joint academic collaboration.

Writing a text on the subject of impacted teeth involves filtering out the relevant and appropriate conclusions of published studies from the mass of orthodontic literature in general, and specifically honing in on those evidence‐based investigations published in the leading international, peer‐reviewed orthodontic journals. The treatment decisions made in individual cases or in small case series of the treatment of rare conditions cannot, by virtue of their small numbers, be founded on evidence that is other than anecdotal. This does not necessarily negate the validity of the decision to treat the next patient with the same condition in a similar manner. However, it must be understood that the decision can be justified on an empirical basis only and is likely to be dependent on careful patient selection; and it does obligate this and any other author to report the possibility of bias. I have tried to comply with this and hope that I have been successful in my diligence in the examples of treatments elaborated in the text.

In my efforts to produce a readable and understandable narrative, I managed to persuade my brother Laurence (Shmuel) Becker to be responsible for the editing and proofreading of this work. He is a lawyer and is the first to admit that he knows absolutely nothing about orthodontics. His theory was that if he could understand what I have written in this volume and could follow the ideas and the logical sequence, then any orthodontist should be able to read, follow and understand the text and the ideas that I have tried to portray easily and painlessly. And so he has corrected, amended, shuffled words around, relocated sections and substituted my words for others that only a lawyer can produce. (He is probably the only other person who will have read the entire book at least five times over.) For all this, I am greatly in his debt.

The wondrous workings of today’s desktop computers have provided me with the means to write this text, which would never have been possible using the steam‐propelled typewriter. However, my computer has also given me a false sense of security, learned from bitter experience. Many times in the past three years I lost material that I had spent days writing, either because I had failed to save it or because I had ‘copy‐pasted’ these sections into other files, which I promptly and unintentionally deleted. I cannot count the number of times that I called my son‐in‐law, Asher Cohen (also a lawyer), setting him the task of rediscovering them and putting me back into the business of writing. He found them every time, at break‐neck speed. I salute his alacrity and his digital skills!

I closely identify with the legendary Danish pianist and comedian who, at the same advanced age as I am now, was still appearing on stage before large live audiences. At the end of one of his solo performances, Victor Borge acknowledged: ‘I wish to thank my parents for having made this possible and I wish to thank my children for having made it necessary.’

Adrian Becker

Jerusalem, Israel

June 2021